Microsoft has announced that a bug in the Windows 10 1809 USB Type-C Connector System Software Interface (UCSI) software implementation can cause the operating system to shut down slower under certain situations. Windows 10 1903 users, this issue has been fixed in that version and you do not need to worry about it. Microsoft has also stated that this bug does not cause any issues with the normal functionality of the plugged in device, but it is just a bug related to connecting or disconnecting a device during a power down event.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-usb-c-bug-can-cause-os-shutdowns-to-be-slower/